VRSF Race Downpipe BMW X3 X4 M40i B58 G01 G02 Heat ShieldVRSF Race Downpipe BMW X3 X4 M40i B58 G01 G02 Heat Shield The factory downpipe on the B58 X3 M40i and X4 M40i is the single best bolt on upgrade you can make. By eliminating the restrictive catalytic converter and reducing back pressure, the VRSF Race Downpipe delivers faster spool, 25 30 horsepower gains with a tune, and an exhaust note that finally matches what the B58 is capable of. Full 4. 5" SS304 stainless steel with heat shield included.